The number 400 is an integer that follows 399 and precedes 401. It is an even number, meaning it is divisible by 2 without leaving a remainder. In Roman numerals, 400 is represented as CD. This number is often used in various contexts, such as mathematics, science, and everyday counting. In terms of significance, 400 can represent a milestone, such as 400 years in history or 400 meters in athletics. It is also notable in the context of 400 degrees Fahrenheit, which is a high temperature used in cooking. Overall, 400 serves as a versatile number in different fields.